Air conditioning system

ABSTRACT

A supplementary air conditioning system includes an indoor heat exchanger and an outdoor heat exchanger. The indoor heat exchanger is fanless and includes indoor tubes installed so as to be inclined to a ceiling of a room. The indoor tubes make diagonal contact with a high-temperature air zone in an upper part of the room and refrigerant inside the indoor tubes is heated by the air zone so as to boil and vaporize and air in the air zone flows down through the indoor heat exchanger. The external heat exchanger includes outdoor tubes installed outside at a higher position than the indoor tubes and are connected to the indoor tubes via connecting pipes with no compressor therebetween. The outdoor tubes condense and liquefy the refrigerant boiled and vaporized in the indoor tubes and return the refrigerant to the indoor tubes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/956,801, filed Nov. 30, 2010, which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2010-18892, filed Jan. 29, 2010, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an air-conditioning system with lowpower consumption.

BACKGROUND

Japanese Laid-Open Patent Publication No. 2002-277001 discloses a methodwhere a heat exchanger unit is installed to supplement the existingcooling performance of a room and thereby improve total coolingperformance, which includes an improvement in the local coolingperformance of air conditioners and cooling fans provided in informationequipment. By using this method, it is possible to integrally providethe additional cooling performance required to cool informationequipment integrally to the information equipment and air conditionersthemselves, thereby minimizing the modification work required onexisting equipment.

SUMMARY

At an information-related facility such as a data center where a largeamount of information equipment such as servers is installed, in mostcases air conditioning equipment is in operation twenty-four hours aday, three hundred and sixty-five days a year regardless of day andnight and the four seasons. Most of the time, the air-conditioningequipment at an information-related facility operates to cool theinterior. It is therefore important to improve cooling performance andto also reduce the power consumed by cooling.

One aspect of the present invention is a system including an indoor heatexchanger and an outdoor heat exchanger. The indoor heat exchanger isfanless but includes an indoor tube installed so as to be inclined tothe horizontal. Refrigerant inside the indoor tube is heated by ahigh-temperature air zone in a room (interior) so as to boil andvaporize, while air in the high-temperature air zone flows down throughthe indoor heat exchanger. The outdoor heat exchanger includes anoutdoor tube that is installed outside and at a higher position than theindoor tube. The outdoor tube is connected to the indoor tube viaconnecting pipes with no compressor being interposed therebetween,condenses and liquefies the refrigerant that boiled and vaporized at theindoor tube, and returns the refrigerant to the indoor tube.

This system does not include a compressor but this system has theoutdoor tube disposed higher than the indoor tube so that therefrigerant circulates naturally due to the difference in specificgravity between vaporized refrigerant and liquefied refrigerant, therebyproducing a low-energy system that is able to cool the room when theoutdoor (outside) temperature is lower than indoor (inside) temperature.The refrigerant inside the indoor tube is heated by the high-temperatureair zone so as to boil and vaporize, while air in the high-temperatureair zone is cooled and flows downward through the indoor heat exchanger.Accordingly, it is possible to omit an interior fan.

In this system, the indoor tube is disposed non-horizontally thatincludes being disposed vertically. In this system, the indoor tubeshould preferably be disposed so as to be inclined (non-perpendicularly)to the horizontal and in addition the indoor tube should preferably bedisposed so as to be near the ceiling of the room and inclined withrespect to the ceiling. By disposing the indoor tube near the ceilingand inclined to the horizontal or to the ceiling, the indoor tube willmake diagonal contact with the high-temperature air zone across theceiling in the upper part of the room. By doing so, air in thehigh-temperature air zone near the ceiling is cooled and flows downwardthrough the indoor heat exchanger unit more efficiently. Accordingly, itis easy to form a down flow and to improve the cooling efficiency of theroom even when an interior fan is omitted. Even if the indoor tube isinclined without being vertical, it is possible for the refrigerant tocirculate effectively on a route where refrigerant that has condensedand liquefied is supplied to a lower end of the indoor tube andrefrigerant that boiled and vaporized is discharged from the upper endof the indoor tube. Accordingly, it is possible to provide an indoorheat exchanger that has favorable cooling efficiency using naturalcirculation.

The system is capable of cooling a room when the temperature outside islower than the temperature inside, but does not have a great effect inimproving the cooling performance of the data center, for example, thepeak cooling performance. However, since a compressor or interior fan isnot necessary, a cooling effect is achieved using little power orwithout using power at all. This means it is possible to reduce thepower consumption needed by air conditioning that runs twenty-four hoursa day, three hundred and sixty-five days a year.

The indoor heat exchanger is capable of being disposed at an air intakeof a floor-standing air conditioner installed on a floor of the room, oron an air path to the air intake. This makes it possible to reduce theair conditioning load of the floor-standing air conditioner and therebyreduce the power consumption of the air conditioner.

The indoor heat exchanger may be connected to the air intake of thefloor-standing air conditioner via a duct. When the indoor tube iscooling condition, a down flow is formed by the indoor tube that isinclined. Accordingly, even when the floor-standing air conditioner andthe indoor heat exchanger are connected via a duct, increasing ofpressure drop at the air conditioner is avoidable.

The system may include an outdoor fan that forcibly supplies outdoor airto the outdoor tube but does not need to include an outdoor fan. Asystem that includes an outdoor fan should preferably further include acontrol unit that controls the operation of the outdoor fan. The controlunit should preferably include a functional unit (function) thatevaluates a heat absorbing capability (cooling performance) of theindoor tube when the outdoor fan is stopped by one of temporarilystopping the outdoor fan and temporarily running the outdoor fan. Inaddition, the control unit should preferably further include afunctional unit that stops the outdoor fan when the heat absorbingcapability of the indoor tube when the outdoor fan is stopped is notinferior to the heat absorbing capability of the indoor tube when theoutdoor fan is running. By doing so, it is possible to further reducethe power consumed by the outdoor fan.

Also, the control unit should preferably further include a functionalunit that stops the outdoor fan when a difference in power consumptionof an air conditioner installed in the room due to a difference betweenthe heat absorbing capability of the indoor tube when the outdoor fan isstopped and the heat absorbing capability of the indoor tube when theoutdoor fan is running is less than power consumption of the outdoorfan. By doing so, it is possible to reduce power consumption relative tothe cooling performance of the entire system that includes the airconditioner.

Another aspect of the present invention is a method of controlling asystem. The system includes an indoor tube, an outdoor tube, an outdoorfan, and a control unit that controls the outdoor fan. The indoor tubeis installed so as to be inclined to the horizontal, and refrigerantinside the indoor tube is heated by an air zone in a room so as to boiland vaporize. The outdoor tube is installed outside at a higher positionthan the indoor tube, is connected to the indoor tube via connectingpipes without a compressor being interposed therebetween, and condensesand liquefies the refrigerant that has boiled and vaporized in theindoor tube and returns the refrigerant to the indoor tube. The outdoorfan forcibly supplies outdoor air to the outdoor tube. The methodincludes steps of:

1. the control unit evaluating a heat absorbing capability of the indoortube when the outdoor fan is stopped by one of temporarily stopping theoutdoor fan and temporarily running the outdoor fan; and

2. the control unit stopping the outdoor fan if the heat absorbingcapability of the indoor tube when the outdoor fan is stopped is notinferior to the heat absorbing capability of the indoor tube when theoutdoor fan is running.

The method may further include a step of:

3. the control unit stopping the outdoor fan if a difference in powerconsumption of an air conditioner installed in the room due to adifference between the heat absorbing capability of the indoor tube whenthe outdoor fan is stopped and the heat absorbing capability of theindoor tube when the outdoor fan is running is less than powerconsumption of the outdoor fan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overview of an air conditioning system;

FIG. 2 is a flowchart showing control of the air conditioning system;

FIG. 3A is a graph showing the relationship between heat-absorbingcapability and temperature difference, and FIG. 3B is a graph showingthe relationship between heat-absorbing capability and refrigerantevaporation temperature; and

FIG. 4 is a timing chart showing how the air conditioning systemoperates.

DETAIL DESCRIPTION

FIG. 1 shows one example of an air conditioning system of a data center.This air conditioning system 10 uses a space of an underfloor 2 b of araised (access) floor 2 that makes a two-level construction including afloor surface 2 a and an underfloor 2 b, to supply cooling air 61 to aplurality of servers 5 disposed on the floor surface 2 a and therebycool (i.e., control the temperature of) the servers 5 and the room 1.The air conditioning system includes a floor-standing main airconditioning system 20 and a supplementary air conditioning system 11disposed near the ceiling 3 of the room 1. The main air conditioningsystem 20 includes a floor-standing indoor (interior) unit 21 and anoutdoor unit 29. The indoor unit 21 includes an evaporator includingcooling tubes 24, a heater 25, and an interior fan 22. The indoor unit21 takes in air via an intake 23 a at a ceiling side of the indoor unit21, controls the temperature of the air, and expels air (cooling air) 61whose temperature has been controlled into the underfloor space 2 b froman outtake 23 b provided so as to pass through the floor 2. Note thatthe following description will focus on a cooling operation by the airconditioning system 10.

The outdoor unit 29 includes a compressor 26, an outside fan 27, and acondenser 28 including liquefying tubes. In the main air conditioningsystem 20, refrigerant that has been compressed by the compressor 26 iscooled by the condenser 28 using the outside air temperature, and byreducing the pressure and causing the refrigerant to evaporate in theevaporator 24 of the indoor unit 21, the cooling air 61 is generated. Inthe indoor unit 21, the air 65 drawn in from the intake 23 a by theinterior fan 22 is cooled by the evaporator 24 and the resulting coolingair 61 is expelled to the underfloor space 2 b to cool the servers 5. Atthe servers 5, electronic equipment inside the servers 5 is cooled bythe cooling air 61 supplied from the underfloor space 2 b and heated air62 is discharged toward the ceiling 3.

The supplementary air conditioning system 11 includes an indoor heatexchanger (indoor heat exchanger unit) 30 that includes indoor tubes 31disposed at an angle to the ceiling 3 of the room 1 and an outdoor heatexchanger (outdoor heat exchanger unit) 40 that is outside 9 andincludes outdoor tubes 41 installed at a higher position than the indoortubes 31. The indoor heat exchanger 30 does not include a fan. Theoutdoor heat exchanger 40 includes an outside fan 44 that forciblysupplies outside air 8 to the outdoor tubes 41, and a fan motor 45 thatdrives the outside fan 44. In addition, the supplementary airconditioning system 11 includes a control unit 50, which controls thefan motor 45 of the outside fan 44, and connecting pipes (fluidlyconnecting pipes) 58 and 59 that connect (fluidly connect) the indoortubes 31 and the outdoor tubes 41 without a compressor being interposedtherebetween. The connecting pipe 59 supplies refrigerant that hasboiled and vaporized at the indoor tubes 31 to the outdoor tubes 41 andthe connecting pipe 58 supplies the refrigerant that has condensed andliquefied at the outdoor tubes 41 back to the indoor tubes 31.

The indoor tubes 31 of the indoor heat exchanger 30 are installed nearthe ceiling 3 that extends horizontally and the indoor tubes 31 areprovided so as to be inclined with respect to the ceiling 3. That is,the indoor tubes 31 are installed so as to be inclined to thehorizontal. The indoor heat exchanger 30 includes a supply header 32, towhich liquefied refrigerant is supplied, and a discharge header 33 thatcollects vaporized refrigerant, with the plurality of indoor tubes 31being connected to both the supply header 32 and the discharge header33. The discharge header 33 of the indoor heat exchanger 30 is disposedcloser to the ceiling 3 than the supply header 32. This means that theplurality of indoor tubes 31 extend diagonally upward from the supplyheader 32 toward the discharge header 33. The plurality of indoor tubes31 are inclined to the vertical and not parallel to or perpendicular tothe vertical, and are inclined with respect to the ceiling 3. That is,the plurality of indoor tubes 31 are installed directly below theceiling 3 so as to be inclined to the horizontal without being parallelor perpendicular to the horizontal and the plurality of indoor tubes 31are installed so as to be inclined with respect to the ceiling 3 thatextends horizontally.

The indoor heat exchanger 30 also includes a housing 39, inside whichthe indoor tubes 31 are disposed, and, in the same way as the indoortubes 31, the housing 39 is disposed so as to be inclined with respectto the ceiling 3. The upper surface of the housing 39 is a supplyopening 38 a through which air is supplied to the indoor tubes 31, whichmeans that the supply opening 38 a is also inclined with respect to theceiling 3. That is, the supply opening 38 a is inclined with respect tothe vertical and the horizontal. The lower surface of the housing 39 isan outtake 38 b that discharges air that has been cooled by the indoortubes 31, with the outtake 38 b being connected via a duct 37 to theintake 23 a of the floor-standing indoor unit 21.

In this supplementary air conditioning system 11, the indoor heatexchanger 30 is supported via the duct 37 by the floor-standing indoorunit 21. However, it is also possible to suspend the indoor heatexchanger 30 from the ceiling 3 or to support the indoor heat exchanger30 from the floor 2 using an appropriate method.

The indoor tubes 31 of the indoor heat exchanger 30 diagonally contact aregion along the ceiling 3 of the room 1 (that is, a high-temperatureair zone 63 in an upper part of the room 1). The refrigerant inside theindoor tubes 31 is heated by the high-temperature air zone 63 and boilsand vaporizes. Since heat is taken from the high-temperature air zone63, such zone is cooled and air 65 that flows downward (i.e., a downflow) from the region close to the ceiling 3 of the room 1 is produced.This air flow (down flow) 65 flows in a substantially verticaldirection. By disposing the indoor tubes 31 so as to be inclined withoutbeing horizontal or vertical (perpendicular), it is possible for theindoor tubes 31 to effectively contact the high-temperature air zone 63that extends horizontally and to effectively produce the down flow 65.In addition, since the indoor tubes 31 are inclined with respect to theceiling 3, the direction in which air is drawn into the indoor tubes 31is limited to a direction in which the down flow 65 is not produced, anda certain circulating flow 64 that carries air in the high-temperatureair zone 63 across the ceiling 3 and into the indoor heat exchanger unit30 is produced. This means it is possible to eradicate hot spots formedat upper parts of the servers 5 comparatively easily, to promote heatexchange at the servers 5, and to cool the servers 5 even moreeffectively.

Accordingly, in the indoor heat exchanger 30, comparatively hot air 64flows from a substantially horizontal direction across the ceiling 3into the supply opening 38 a and cooled air 65 is discharged in asubstantially vertical direction from the outtake 38 b. The air 65 thathas been discharged from the indoor heat exchanger 30 is drawn in fromthe intake 23 a of the floor-standing indoor unit 21, is cooled further,and then supplied to the servers 5. Accordingly, in a condition wherethe supplementary air conditioning system 11 is in operation, the loadof the main air conditioning system 20 can be reduced, thereby reducingthe power consumption of the main air conditioning system 20.

Due to the difference in specific gravity with liquid refrigerant, therefrigerant that has boiled and vaporized in the indoor tubes 31 of theindoor heat exchanger 30 of the supplementary air conditioning system 11rises within the tubes and is collected in the discharge header 33disposed at the top, then passes through the connecting pipe 59 andreaches the outdoor heat exchanger unit 40 that is positioned evenhigher. At the outdoor heat exchanger 40, the vaporized refrigerant thathas flowed into the outdoor tubes 41 is cooled by the outside air andcondenses and liquefies to become liquid refrigerant. Due to thedifference in specific gravity with the vaporized refrigerant, theliquid refrigerant flows downward via the connecting pipe 58 to thesupply header 32 of the indoor heat exchanger unit 30 positioned below.In this way, in the supplementary air conditioning system 11, by causingthe refrigerant to circulate naturally under gravity due to thedifference in specific gravity between liquid refrigerant and vaporizedrefrigerant without using a compressor or a pump, it is possible toexpel heat from the room 1 into the outside air. Accordingly, power(i.e., electricity) for driving a compressor is not required in thesupplementary air conditioning system 11.

Typical examples of the indoor tubes 31 and the outdoor tubes 41 arealuminum pipes or copper pipes, and such pipes may be equipped with finsor may be finless. The fins may be corrugated, plate-like, or in theform of spines. The refrigerant may be any refrigerant that vaporizes atroom temperature and liquefies at outside air temperature as operatingconditions, and as one example, HFC134a (whose chemical formula isCH₂FCF₃) may be used.

In addition, the air flows 64 and 65 in the room 1 produced by theindoor tubes 31 that are disposed at an angle in the supplementary airconditioning system 11 cause the air in the room 1 to circulate andeffectively come into contact with the indoor tubes 31. Accordingly, thesupplementary air conditioning system 11 does not need an indoor fan andpower (i.e. electricity) required by such an indoor fan is not required.

In the supplementary air conditioning system 11, the indoor heatexchanger 30 is connected to the intake 23 a of the indoor unit 21 ofthe main air conditioning system 20 by the duct 37 and the power of thefan 22 of the indoor unit 21 is used to ensure that air circulates.However, when the indoor heat exchanger 30 is in operation, the load ofthe interior fan 22 of the indoor unit 21 is reduced by the down flow 65produced by the indoor heat exchanger 30.

It is also possible to reduce the cooling load of the main airconditioning system 20 by disposing the indoor heat exchanger 30 of thesupplementary air conditioning system 11 on a path taken by room airdrawn in by the intake 23 a of the indoor unit 21 of the main airconditioning system 20 without connecting the indoor heat exchanger unit30 via the duct 37. It should be noted that the supplementary airconditioning system 11 reduces the thermal load of the room 1 by itself,for example by disposing the indoor head exchangers 30 separately to theindoor unit 21 and distributing the exchangers 30 among a number oflocations in the room 1.

In the outdoor heat exchanger 40, while the outside fan 44 that isrotated using the motor 45 is equipped, the outdoor tubes 41 is alsocooled using external air (i.e., the wind outside) by stopping theoutside fan 44. In particular, when cooling a building erected in alandscape where the wind blows constantly, in many cases there will beno need to drive the outside fan 44 using the motor 45. For example, inan environment where a large number of buildings are erected in a row, asufficient cooling effect may be obtained by winds that pass between thebuildings. If the fan motor 45 is not running, no power (electricity)will be required, which means that the supplementary air conditioningsystem 11 is capable of cooling the room 1 with fundamentally no powerconsumption. Accordingly, it is possible to further reduce the powerrequired to cool the room 1 that is used as a data center or the like.

On the other hand, when there is no wind or the force of the wind isinsufficient, there are cases where running the motor 45 of the outsidefan 44 to make use of the cooling ability of the supplementary airconditioning system 11 will reduce the power consumption of the entireair conditioning system 10. Data centers in particular consume hugeamounts of power, resulting in demand for every possible improvement inpower consumption. Data centers operate continuously for twenty-fourhours a day, three hundred and sixty-five days a year, so that thesupplementary air conditioning system (heat-discharging unit,heat-discharging system) 11 will also operate for a considerable timeand assists in reducing the power consumption and operating time of theair conditioning system 10. So, any reducing power consumption isimportant. In addition, in a system operating throughout the year, sincethe life of the motor 45 is related to the cumulative operating time(normally around 20,000 hours), if the operating time of the fan motor45 can be suppressed, it will be possible to extend a maintenance cyclethat includes replacing the motor, and thereby reduce the cost.

For this reason, the control unit 50 of the supplementary airconditioning system 11 includes a function (evaluation function,evaluation functional unit) 51 for evaluating the performance (i.e., theheat absorbing capability of the internal tubes) when the outside fan 44is running, and first and second functions (functional units) 52 and 53that stop (i.e., do not run) the motor 45 of the outside fan 44 underpredetermined conditions. The evaluation function 51 temporarily stopsthe outside fan motor 45 or temporarily runs the outside fan motor 45and evaluates the cooling performance of the indoor heat exchanger unit30, that is, the heat absorbing capability of the indoor tubes 31 whenthe outside fan motor 45 is stopped and that of when the outside fanmotor 45 is running. The first stopping function 52 stops the outsidefan 44 if the heat absorbing capability of the indoor tubes 31 when theoutside fan 44 has stopped is not inferior to the heat absorbingcapability of the indoor tubes 31 when the outside fan 44 is running.The second stopping function 53 stops the outside fan 44 (the fan motor45) if a reduction in power consumption (difference in powerconsumption) of the main air conditioning system 20 due to a differencebetween the heat absorbing capability of the indoor tubes 31 when theoutside fan 44 is running and the heat absorbing capability of theindoor tubes 31 when the outside fan 44 is stopped is smaller than thepower consumption of the motor 45 of the outside fan 44.

FIG. 2 is a flowchart showing the operation of the control unit 50.First, in step 71, the evaluation functional unit 51 judges theevaluation timing. A first method for judging the evaluation timing iswhether a predetermined period has passed. Another method for judgingthe evaluation timing is whether a parameter (measurement value) set inadvance for evaluating the performance of the indoor heat exchanger 30has reached a threshold value.

When the evaluation timing has been reached, in step 72, the evaluationfunctional unit 51 judges whether the outside fan 44 (the fan motor 45)is running and if the outside fan 44 is running, stops the outside fan44 in step 73 and evaluates the performance of the indoor heat exchanger30. That is, the heat absorbing capability of the indoor tubes 31 isevaluated. On the other hand, if the outside fan 44 is stopped, in step74 the outside fan 44 (the fan motor 45) is run and the heat absorbingcapability of the indoor tubes 31 is evaluated.

The performance of the indoor heat exchanger 30, that is, the heatabsorbing capability of the indoor tubes 31 is evaluated as follows.FIG. 3A shows the relationship between the temperature difference ΔT1(°C.) between input air and output air of the indoor heat exchanger 30 andthe heat absorbing capability (kW). FIG. 3B shows the temperature T2(°C.) of vaporized refrigerant in the indoor heat exchanger 30. Each ofthese parameters (measurement values) changes substantiallyproportionally to the heat absorbing capability of the indoor tubes 31.Accordingly, by measuring one of such parameters in step 73 or 74 andcomparing with the parameter in the previous state, that is, theparameter when the outside fan 44 (the fan motor 45) was on or off, itis possible to evaluate the performance (cooling performance) of theindoor heat exchanger unit 30 when the outside fan 44 is on and off.

If, in step 75, the first stopping function 52 finds that theperformance (heat absorbing capability, OFF performance) Qoff of theindoor heat exchanger 30 when the outside fan 44 is off is not inferiorto the heat absorbing capability (ON performance) Qon when the outsidefan 44 is on, that is, if Condition (1) is satisfied, the first stoppingfunctional unit 52 stops the outside fan 44 (the fan motor 45) in step78.

Qon≦Qoff  (1)

When the heat absorbing capability is the same, the outside fan 44 isstopped to suppress the power consumption of the supplementary airconditioning system 11.

When the heat absorbing capability of the indoor heat exchanger 30 ishigher when the outside fan 44 is on, the second stopping functionalunit 53 further judges whether a difference ΔPw in power consumption ofthe main air conditioning system 20 due to the difference ΔQ between theheat absorbing capability of the indoor heat exchanger 30 when theoutside fan 44 has stopped and the heat absorbing capability of theindoor heat exchanger 30 when the outside fan 44 is running is equal toor below the power consumption of the outside fan 44 (the powerconsumption of the fan motor 45) Pf.

The difference in performance (difference in heat absorbing capability)ΔQ can be calculated according to Equation (2) below using the airflowvolume V (m³/h), the weight volume ratio γ(kg/m³), the specific heat(kcal/kg° C.), the difference in temperature ΔT1(° C.) between the inputair and output air of the indoor heat exchanger unit 30, and a value (1kW=860 kcal/h) for converting 1 kW to calories (kcal). The airflowvolume V is the volume of air that passes the indoor heat exchanger 30(the indoor tubes 31), and in this example, is the volume of air drawnin by the indoor unit 21.

ΔQ=V·γ·Cp·ΔT1/(0.86)  (12)

The difference ΔPw in power consumption of the main air conditioningsystem 20 that includes the indoor unit 21 due to such difference inperformance ΔQ can be calculated according to Equation (3) using thecooling efficiency (or coefficient of performance (COP)) (coolingperformance kW/power consumption kW).

ΔPw=ΔQ/COP  (3)

Accordingly, if Condition (4) below is satisfied in step 76, the secondstopping functional unit 53 stops the outside fan 44 in step 78.Conversely, if Condition (4) is not satisfied, the outside fan 44 is runin step 77.

ΔPw≦Pf  (4)

Here, Pf is the power consumption of the fan motor 45 that drives theoutside fan 44. If there is no difference in power consumption, themotor 45 of the outside fan 44 is stopped to suppress the operating timeof the motor 45.

FIG. 4 is a timing chart showing one example of the operation of thesupplementary air conditioning system 11. When the evaluation timing isreached at time t1, since the outside fan 44 was running before time t1,the evaluation functional unit 51 stops the outside fan 44 and evaluatesthe performance (heat absorbing capability) of the internal (interior)heat exchanger unit 30. If the evaluation period has elapsed and thereis no change in the heat absorbing capability of the indoor heatexchanger unit 30 at timing t2 in spite of the outside fan 44 havingstopped, the first stopping function 52 stops the outside fan 44.

At this time, the evaluation functional unit 51 sets a threshold Tth forre-evaluating the performance of the indoor heat exchanger unit 30, thatis, the heat absorbing capability of the indoor tubes 31. For example,if a measurement value for evaluating the performance is the refrigerantevaporation temperature T2, a temperature that is around one degreehigher than the evaporation temperature T2 during the evaluation periodis set as the threshold Tth. If the measurement value for evaluating theperformance is the temperature difference ΔT1, a temperature that isaround one degree lower than the temperature difference ΔT1 during theevaluation period is set as the threshold Tth.

At timing t3 when a predetermined period has elapsed from the previousevaluation, since the outside fan 44 was not running before timing t3,the evaluation functional unit 51 runs the outside fan 44 and evaluatesthe heat absorbing capability of the indoor (interior) heat exchangerunit 30. When the evaluation period has elapsed, if the first stoppingfunctional unit 52 judges at timing t4 that the performance of theindoor heat exchanger unit 30 is higher and the second stoppingfunctional unit 53 further judges that the reduction in powerconsumption of the main air conditioning system 20 is at least equal tothe power consumption of the fan motor 45, the outside fan 44 is run attiming t4 (the running of the outside fan 44 continues).

After time has passed again and the evaluation timing is reached attiming t5, since the outside fan 44 was running before timing t5, theevaluation functional unit 51 stops the outside fan 44 and evaluates theheat absorbing capability of the indoor (interior) heat exchanger unit30. When the evaluation period has elapsed, if at timing t6 there is nodifference in the heat absorbing capability of the indoor heat exchangerunit 30 in spite of the outside fan 44 having stopped, the firststopping functional unit 52 stops the outside fan 44 (i.e., the outsidefan 44 is not run).

If the evaporation temperature T2 of the indoor tubes 31 of the indoorheat exchanger unit 30 reaches the threshold Tth at timing t7, eventhough little time has passed, since the state of the outside air haschanged, the evaluation functional unit 51 runs the outside fan 44 andevaluates the heat absorbing capability of the indoor heat exchangerunit 30 (the indoor tubes 31). After the evaluation period has passed,the first stopping functional unit 52 judges at timing t8 that the heatabsorbing capability of the indoor heat exchanger unit 30 is higher whenthe outside fan 44 is running. However, if the second stoppingfunctional unit 53 judges that the difference (in this case, increasing)ΔPw in power consumption of the main air conditioning system 20 issmaller than the power consumption Pf of the fan motor 45, the outsidefan 44 is stopped from timing t8 onwards to reduce the overall powerconsumption of the entire air conditioning system 10.

The air conditioning system 10 that controls the room temperature of theroom 1 of this data center includes the main air conditioning system 20and the supplementary air conditioning system 11 that uses naturalcirculation and, during the night or in seasons aside from summer wherethe outside air temperature is low, is able to discharge heat frominside the room 1 using the supplementary air conditioning system 11using very little or no power at all. Accordingly, the thermal load ofthe main air conditioning system 20 can be reduced and the powerconsumption of the air conditioning system 10 that includes the main airconditioning system 20 can be reduced.

In particular, the supplementary air conditioning system 11 according tothe present embodiment does not include an indoor fan and also stops theoperation of the outdoor fan whenever possible, which makes it possibleto discharge heat from inside the room 1 to the outside using the leastpossible power. This means that the supplementary air conditioningsystem 11 is capable of cooling the room 1 using outside air temperatureas a natural energy source and also using natural winds, such as breezesbetween buildings, as an energy source. On the other hand, whenintermittent energy in the form of wind cannot be used, by driving theoutside fan 44, it is possible to improve the usage efficiency ofnatural energy in the form of outside air. This means that it ispossible to reduce power consumption more thoroughly. Also, by reducingthe operation ratio of the fan motor 45, it is possible to reduce thecost required for maintenance.

Note that although an example is described above where the indoor heatexchanger (indoor heat exchanger unit) 30 is installed in a room 1 witha ceiling 3 that extends horizontally, it is also possible to installthe indoor heat exchanger 30 into a room with a ceiling that is inclinedto the horizontal. In such case, the indoor tubes 31 is installed so asto be inclined to or perpendicular (i.e., vertical) to the horizontal.In addition, the indoor tubes 31 should preferably be installed so as tobe inclined to the ceiling 3 that is inclined to the horizontal. Thismakes it easy to provide a sufficient contact area for thehigh-temperature air zone present across the ceiling 3. The indoor tubes31 may also be disposed so as to be vertical. However, to suppress adrop in the contact effectiveness between the indoor tubes 31 andhigh-temperature air due to vertical down streams, the indoor tubes 31should preferably be installed so as to be inclined to the vertical.

Also, although an example of an air conditioning system installed in adata center has been described above, the cooling load for the presentinvention is not limited to information equipment such as servers. Theair conditioning system according to the present invention is alsosuited to regulating temperature in conditions where it is not possibleto open a window to let in breezes, such as when regulating temperaturein a clean room. In addition, although a system according to the presentinvention has been described for an example where the system is combinedwith a floor-standing air conditioning system, it is also possible touse the system according to the present invention alone, in combinationwith another type of air conditioning system, in combination with anexisting air conditioning system, or a variety of other methods inaccordance with the conditions and environment that require airconditioning.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1-10. (canceled)
 11. A system comprising: an indoor heat exchanger thatis a fan-less heat exchanger and includes an indoor tube installed so asto be inclined to the horizontal, the indoor tube contacting ahigh-temperature air zone in an upper part of a room and refrigerant inthe indoor tube being heated by the high-temperature air zone so as toboil and vaporize with air in the high-temperature air zone flowing downthrough the indoor heat exchanger: an outdoor heat exchanger thatincludes an outdoor tube installed outside at a higher position than theindoor tube, the outdoor tube being connected to the indoor tube viaconnecting pipes without a compressor being interposed therebetween andthe outdoor tube condensing and liquefying the refrigerant boiled andvaporized in the indoor tube and returning the refrigerant to the indoortube: and a floor-standing air conditioner installed on a floor of theroom, wherein the indoor heat exchanger is disposed so as to directlycontact the high-temperature air and a down flow produced by the indoorheat exchanger is drawn into an air intake of the floor-standing airconditioner.
 12. The system according to the claim 1, wherein the indoortube is installed so as to be inclined with respect to a ceiling of theroom.
 13. The system according to the claim 1, wherein the indoor heatexchanger is connected via a duct to the air intake of thefloor-standing air conditioner.